The present invention relates to methods and apparatus for conditioning of polishing pads used in planarizing substrates.
Chemical-mechanical planarization (xe2x80x9cCMPxe2x80x9d) processes remove material from the surface of semiconductor wafers or other substrates in the production of microelectronic devices and other products. CMP processes typically planarize and/or polish the surface of the substrate in the fabrication of integrated circuits by moving the substrate across a polishing medium to remove material from the substrate surface.
FIG. 1 is a schematic view that illustrates a conventional CMP machine 10 with a platen 20, a wafer carrier 30, a polishing pad 40, and a planarizing liquid 44 on the polishing pad 40. The platen 20 is typically connected to a drive assembly 26 to rotate the platen 20 (indicated by arrow A) or reciprocate the platen 20 back and forth (indicated by arrow B). Additionally, the wafer carrier 30 generally has a lower surface 32 to which one or more wafers 12 may be attached, or the wafers 12 may be attached to resilient pads 34 positioned between the wafers and the lower surface 32. The wafer carrier 30 is generally attached to an actuator assembly 36 to impart axial and/or rotational motion to the wafers 12 (indicated by arrows C and D, respectively), or the wafer carrier 30 may be a weighted, free-floating wafer holder (not shown).
The polishing pad 40 and the planarizing liquid 44 may separately, or in combination, define a polishing medium that mechanically and/or chemically removes material from the surface of a wafer. The polishing pad 40 may be a conventional polishing pad made from a continuous phase matrix material (e.g. polyurethane), or it may be a new generation abrasive polishing pad made from abrasive particles fixedly dispersed in a suspension medium. Conversely, the planarizing liquid 44 may be a conventional CMP slurry with abrasive particles, or it may be a planarizing solution without abrasive particles. In general, abrasive slurries are used with conventional non-abrasive polishing pads and planarizing solutions are used with abrasive polishing pads.
To planarize the wafers 12 with the CMP machine 10, the wafer carrier 30 presses the wafers 12 face-downward against the polishing medium. More specifically, the wafer carrier 30 generally presses the wafers 12 against the planarizing liquid 44 on a planarizing surface 42 of the polishing pad 40, and at least one of the platen 20 or the wafer carrier 30 moves relative to the other to move the wafers 12 across the planarizing surface 42. As the wafers 12 move across the planarizing surface 42, material is removed from the face of the wafers. The process is conventionally conducted at platen temperatures of approximately 85xc2x0 F. to 105xc2x0 F. to facilitate any chemical interaction between the polishing medium and the wafer 12. Conventional wisdom is that processing at higher temperatures may cause undesirable chemical interactions between the polishing medium and the wafer 12. Furthermore, where ammonia-based slurries are used, higher temperatures may cause the ammonia to evaporate, creating undesirable odors and potentially shifting the pH of the slurry by an unacceptable amount.
In the competitive semiconductor industry, it is desirable to maximize the through-put of finished wafers and to produce a uniform, planar surface on each wafer. The through-put of CMP processing is a function of several factors, one of which is the rate at which the thickness of the wafer decreases as it is being planarized (the xe2x80x9cpolishing ratexe2x80x9d). The polishing rate affects the through-put because the polishing period per wafer decreases with increasing polishing rates and it is easier to accurately endpoint CMP processing with a consistent polishing rate. Thus, it is desirable to have a high, consistent polishing rate.
One manufacturing concern with CMP processing is that the through-put may drop because the act of planarizing wafers alters the condition of the polishing pads. More specifically, slurry and particles from the wafer and pad build up on the planarizing surface of the polishing pad and form waste matter accumulations that may cover portions of the planarizing surface. The accumulations may take the form of a hard glaze coating on the planarizing surface which reduces contact between the wafer and the planarizing surface. The polishing rate accordingly changes during CMP processing, which may make it more difficult to quickly planarize a wafer or endpoint the CMP process. Thus, the waste matter accumulations may reduce the through-put of CMP processing.
CMP processes must also consistently and accurately produce a uniform, planar surface on the wafer because it is important to accurately focus the image of circuit patterns on the surface of the wafer. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the circuit pattern to within a tolerance of approximately 0.1 xcexcm. Focusing circuit patterns to such small tolerances, however, is very difficult when the surface of the wafer is not uniformly planar. Thus, planarizing processes must create a highly uniform, planar surface.
Another problem with CMP processing is that the waste matter accumulations reduce the uniformity of the polishing rate across the planarizing surface of a polishing pad. The waste matter accumulations do not build up uniformly across the planarizing surface of the polishing pad, and thus the polishing rate may vary unpredictably across the polishing pad. As a result, the surface of a polished wafer may not be uniformly planar.
The problems associated with waste matter accumulations are exacerbated when the planarizing surface simultaneously planarizes a large number of wafers or when the planarization rate is increased. For example, FIG. 1 illustrates a single wafer carrier 30 to which are attached several wafers 12, each of which contributes waste matter accumulations to the planarizing surface. In other conventional CMP machines, multiple wafer carriers, each with multiple wafers, further increase the rate at which waste matter accumulates on the planarizing surface. As the number of wafers planarized by a given planarizing surface increases, the rate at which waste matter accumulates on the planarizing surface also increases, decreasing wafer through-put and wafer uniformity.
In light of the problems associated with waste matter accumulations on polishing pads, it is necessary to periodically remove the waste matter accumulations from the planarizing surfaces so that the polishing pads are brought back into a desired state for planarizing substrates (xe2x80x9cconditioningxe2x80x9d). For example, U.S. Pat. No. 5,456,627 issued to Jackson et al. discloses an apparatus for conditioning a rotating, circular polishing pad with a rotating end effector that has an abrasion disk in contact with a polishing surface of the pad. The end effector described in U.S. Pat. No. 5,456,627 moves along a radius of the polishing pad surface at a variable velocity to compensate for the linear velocity of the polishing pad surface. Additionally, U.S. Pat. No. 5,456,627 discloses maintaining a desired contact force between the end effector and the polishing pad surface with a closed feedback loop in which a load transducer generates a signal with an amplitude proportional to the applied force. A computer then uses the signal from the load transducer to operate an actuator that moves the end effector in a direction so that the output of the load transducer is substantially equal to the desired contact force.
Another conventional conditioning method and apparatus, which is disclosed in U.S. Pat. No. 5,081,051 issued to Mattingly et al., uses an elongated blade with a serrated edge that is engaged with a portion of a circular, rotating polishing pad. The blade disclosed in U.S. Pat. No. 5,081,051 is pressed against a polishing path on the planarizing surface of the polishing pad to scrape or cut grooves into the planarizing surface.
Conventional conditioning methods and devices, however, take time to condition the pad because they abrasively wear away or cut through waste matter accumulations which have formed a hardened glaze on the planarizing surface. Additionally, conventional conditioning methods and devices may result in a non-planar surface on the polishing pads. Therefore, it would be desirable to develop a method and apparatus that reduces the time required to condition the polishing pads and improves the quality of the conditioned pads.
The present invention is directed, in part, toward a method and apparatus for controlling a polishing characteristic of a polishing pad used in planarization of a substrate. In one embodiment of the method, the temperature of a planarizing surface of the polishing pad is controlled to be at least approximately 98% of a glass transition temperature of polishing pad material comprising the polishing pad. The method further comprises removing material from the planarizing surface. The method may further comprise removing a predetermined thickness of the polishing pad to further control the polishing characteristic of the polishing pad. In one embodiment of the invention, the temperature of the planarizing surface is controlled by electrically heating a support surface supporting the polishing pad. In an alternate embodiment, the planarization surface is positioned within an insulated enclosure and is heated by heating the air within the enclosure proximate to the planarizing surface. In further alternate embodiments of the invention, the planarizing surface is heated directly. In one such embodiment, heated air is directed toward the planarizing surface. In another such embodiment, a heated planarizing liquid is directed toward the planarizing surface. The heated planarizing liquid both heats the planarizing surface and the waste matter accumulations thereon and, in one embodiment, aids in chemically-mechanically planarizing the substrates.